Short-Term Frequency Stability of Relaxation Crystal Oscillators

Due to the need for stable frequency rectangular wave signals, various relaxation quartz crystal oscillators were designed. Therefore it is of interest to have data on their short-term frequency stability. The generally accepted definitions of measures for short-term frequency stability and measurement procedures are reviewed in this paper. Measurement results for the short-term frequency stability of quartz crystal multivibrators in time and frequency domains show a high spectral purity of the multivibrator output signal. The single-sideband-to-carrier phase noise has values lower than -90 and -120 dB on the offset frequencies of 1 and 10 Hz, respectively. The white phase noise is about -160 dB. The power law spectral density model of fractional frequency fluctuations for the quartz multivibrators is established and a discussion on the noise sources is given.     

Relaxation Properties of the Trapped Flux of Bulk High-Temperature Superconductors at Different Magnetization Levels

The magnetic relaxation phenomenon is a crucial subject for the engineering applications of bulk high-temperature superconductors (HTS) in which the trapped field or levitation force behaves with a time-dependent decay due to the intrinsic flux creep inside the HTS materials. To fully exploit the high trapped field of bulk HTS, we have experimentally investigated the trapped flux relaxation properties, especially at different magnetization levels. With different excitation fields, the dependence between trapped field and relaxation rate was analyzed and compared in both field-cooling magnetization (FCM) and zero-field-cooling magnetization (ZFCM) conditions. In parallel, the relaxation rates for different trapped flux can be measured all at once during a single magnetization process. The relaxation rate is closely correlated to the trapped field and useful to reflect the effect of the following remagnetization processes. To suppress the relaxation, we further checked possible methods from the three aspects of material improvement, working temperature and flux annealing effect.     

ZnGeP2晶体点缺陷的研究进展

ZnGeP2晶体是具有重要应用背景的红外非线性光学材料.晶体中的点缺陷严重限制了ZnGeP2晶体的应用发展.本工作介绍了ZnGeP2晶体点缺陷的最新研究进展情况.首先,利用电子顺磁共振技术研究了ZnGeP2晶体的点缺陷.主要存在缺陷是受主缺陷V-Zn及施主缺陷VOP和Ge Zn,其相应的缺陷能级分别为E(V-Zn)=EC-(1.024±0.03)eV,E(VOP)=EV (1.61±0.06)eV和E(Ge Zn)=EV (1.70±0.03)eV.对晶体作了电子照射及高温退火等处理后,又分别发现了两种缺陷V3-Ge和Vpi.其次,利用全势能线性muffin-tin轨道组合法模拟研究了ZnGeP2晶体的点缺陷.主要存在缺陷及缺陷能级的计算结果与实验结果基本一致,但由于理论模拟与实际情况还存在差距,有些计算结果与实验结果相矛盾.因此,将实验与理论有机结合研究晶体的点缺陷是今后研究的重点.     

Origin of Magnetism from Native Point Defects in ZnO

Based on the first-principle calculations by using the Korringa?CKohn?CRostoker coherent potential approximation (KKR-CPA) method in connection with the local density approximation (LDA), we study theoretically the electronic and magnetic properties of different point defects in ZnO, which are Zinc interstitials (Zn_i), Zinc antisites (Zn_O), Oxygen interstitials (O_i) and Oxygen antisites (O_Zn) defects in ZnO. The supercell calculations were also performed using the full potential local-orbital (FPLO) band structure scheme. This work presents detailed information about total and local density of states at some concentrations of these defects; the stability of the ferromagnetic state compared with the spin-glass state is investigated by comparing calculating their total energy. The results show on one hand that Zn_i and Zn_O produce a shallow donor bellow the bottom of the conduction band (CB), while O_i and O_Zn produces the shallow acceptors above the top of the valence band (VB), and moment magnetic; on other hand that the ferromagnetic state is more stable than the spin-glass in Oxygen interstitials (O_i) and vice versa for oxygen antisites (O_Zn) of native point defects in ZnO. The other native point defects (Zn_i, Zn_O, V_O, and V_Zn) have a zero magnetic moment. The results show that the Curie temperature increases with the concentration of interstitial oxygen.     

Superconducting Point Defect in a Two-Dimensional Photonic Crystal

This paper presents the tunability of the high temperature superconducting (SC) point defect modes in a two-dimensional photonic crystal composed of circular cylinders on a square lattice. By some modifications on the plane wave expansion method, we have shown that the properties of the SC point defect modes strongly depend on the temperature and external magnetic fields. The superconductor type and the nearest-neighbor of the defect effects are further investigated. Comparison between SC and conventional defects show that the SC one has only a monopole profile for different values of the defect size, and has very low sensitivity on the disorders, which is an important feature from a manufacturing point of view.     

Magnetic and Electronic Properties of Point Defects in ZrO2

Using the Korringa–Kohn–Rostoker Coherent Potential Approximation (KKR-CPA) method in connection with the Generalized Gradient Approximation (GGA), we study the magnetic and electronic properties of different point defects in cubic ZrO₂. In particular, we discuss the zirconium interstitial (Zr_i), zirconium antisite (Zr_O), zirconium vacancy (V_Zr), oxygen interstitial (O_i), oxygen antisite (O_Zr), and oxygen vacancy (V_O) defects. It has been shown that oxygen vacancy and zirconium interstitial (V_O, Zr_i) are n-type, while the other point defects are p-type. The magnetic moments are observed only in the oxygen interstitial and antisite (O_i, O_Zr) cases. The corresponding ferromagnetic states are more stable than the spin–glass states. It has been found that the mechanism responsible of such stabilities is the double exchange. Based on Mean Field Approximation (MFA), the Curie temperature (T _C ) is estimated. Moreover, it has been found that the O_i and O_Zr defects provide half-metallic properties being the responsible for ferromagnetism.     

合成金刚石晶体缺陷的同步辐射形貌研究

采用同步辐射白光貌相术研究合成金刚石单晶体中的晶体缺陷,观察到晶体中存在籽晶,籽晶周围存在着大量的位错线.位错线起源于籽晶表面,终止于晶体表面.计算了位错束的空间走向和位错密度.分析了晶体的生长阶段和影响晶体缺陷的主要因素,指出通过减少籽晶表面的缺陷,保持生长条件的稳定,能够有效地降低合成金刚石晶体中缺陷的密度,提高合成金刚石晶体的完整性.     

天然金刚石晶体缺陷的同步辐射形貌研究

本文利用北京同步辐射白光形貌术研究了辽宁天然金刚石晶体的缺陷问题，实验结果表明，金刚石晶体中存在有位错，生长带和生长带和孪晶等缺陷，文中对位错进行了详细讨论，并确定其特征量。     

3D Point Cloud Analysis for Detection and Characterization of Defects on Airplane Exterior Surface

Three-dimensional surface defect inspection remains a challenging task. This paper describes a novel automatic vision-based inspection system that is capable of detecting and characterizing defects on an airplane exterior surface. By analyzing 3D data collected with a 3D scanner, our method aims to identify and extract the information about the undesired defects such as dents, protrusions or scratches based on local surface properties. Surface dents and protrusions are identified as the deviations from an ideal, smooth surface. Given an unorganized point cloud, we first smooth noisy data by using Moving Least Squares algorithm. The curvature and normal information are then estimated at every point in the input data. As a next step, Region Growing segmentation algorithm divides the point cloud into defective and non-defective regions using the local normal and curvature information. Further, the convex hull around each defective region is calculated in order to englobe the suspicious irregularity. Finally, we use our new technique to measure the dimension, depth, and orientation of the defects. We tested and validated our novel approach on real aircraft data obtained from an Airbus A320, for different types of defect. The accuracy of the system is evaluated by comparing the measurements of our approach with ground truth measurements obtained by a high-accuracy measuring device. The result shows that our work is robust, effective and promising for industrial applications.     

天然金刚石晶体缺陷与性能的研究

利用红外光谱和X射线形貌术等方法对辽南天然金刚石晶体进行了晶体类型、缺陷及性能的研究。结果发现,有的晶体存在有各种缺陷,如位错、亚结构或孪晶界等。对部分位错做了详细地讨论,并确定其特征量,同时还发现,晶体中位错的存在对其透光性能有明显的影响。     

The Condition for Existence of Complex Modes in Trapped Bose–Einstein Condensate with a Highly Quantized Vortex

We consider a trapped Bose–Einstein condensate with a highly quantized vortex. Pu et al. found numerically the parameter region in which complex eigenvalues arise. Recently, the splitting of a highly quantized vortex into two singly quantized vortices is observed in the experiment. We derive analytically the condition for the existence of complex eigenvalues by using the small coupling constant expansion and the two-mode approximation. We check that our results agree with those by Pu et al.     

Coupled Phonon-Ripplon Modes in the Electron Crystal at Different Driving Fields

Coupled phonon-ripplon oscillations in a two-dimensional electron crystal over liquid helium with surface electron density n _s =1.2×10⁹ cm⁻² at the temperature T=83 mK are studied in a Corbino experimental cell. The measurements are performed in the frequency interval where resonances of the coupled oscillations are observed and at different driving voltages V _∥ <10 mV at which nonlinear features in the crystal conductivity start to appear. A special attention is paid to a relatively narrow frequency interval ω/2π≃3–5 MHz. In this interval the jumps in the oscillation spectrum are observed. From the data obtained, the mobility and electron effective mass are calculated as functions of driving electric field. The electron effective mass in the crystal and dissipative losses are found to increase with the driving field increase. A possible reason for that can be an anharmonicity of the electron-ripplon interaction, which become noticeable if the electron crystal velocity along the surface is high enough.     

Charge State of Indium and Point Defects in Indium-Doped Lead Telluride Crystals

Experimental data on the lattice parameter, thermoelectric power, and microhardness of PbTeIn crystals and the conversion fromp- to n-type with increasing indium content can be interpreted under the assumption that the indium in PbTeIn has variable valence: 2In²⁺ In⁺ + In³⁺. A crystal-quasi-chemical model is proposed for defect formation in PbTeIn: the incorporation of In⁺ into octahedral interstices and In³⁺ into tetrahedral interstices of the close packing of Te atoms, accompanied by In₂Te₃ precipitation.     

Acoustic Modes and Momentum Relaxation in 2D Atomic Hydrogen on Helium Surface

Seeking for manifestations of superfluidity in 2D spin-aligned atomic hydrogen (H↓) adsorbed on the surface of liquid helium at T∼0.1 K we consider possible acoustic modes in this 2D Bose gas depending on frequency and on characteristic times of energy and momentum transfer. At high frequencies, the analogues of ordinary and second sound are realized in 2D H↓. At low frequencies, the 2D analogue of the fourth sound is realized: the normal component of hydrogen and ripplons are immobile and only the superfluid component of hydrogen participates the oscillations. We also estimate the rate of momentum relaxation between superfluid hydrogen and ripplons, τ _HR⁻¹ ∝ T ^13/3. The most promising for observing the superfluidity in 2DH↓ is the fourth sound, which could be excited, e.g., by ESR.     

氧化锌中的本征点缺陷对材料光电性能的影响

ZnO薄膜中的本征点缺陷对材料的电学、发光性能有着至关重要的影响.目前,对本征点缺陷的研究是ZnO领域的一大热点,也是实现ZnO基光电器件的关键技术之一.本文结合最新研究,扼要综述了本征点缺陷的电荷特性、对本征ZnO为n型的作用机理、对p型ZnO制备的影响及点缺陷对薄膜绿光发光的贡献.     

Modeling of Point Defects in Cl-Doped CdTe Crystals Annealed in Cd Vapor

Equations are proposed for quasi-chemical reactions leading to the formation of intrinsic and impurity defects and defect complexes in Cl-doped cadmium telluride crystals during annealing in cadmium vapor at different temperatures. The equilibrium constants for the formation of (Cl _Te ⁺ V _Cd ²⁻ )⁻ defect complexes and Te _Cd ²⁺ antisite defects are calculated. An analytical expression is derived for the cadmium partial pressure corresponding to a type conversion. The conditions are established for producing n- and p-type CdTe〈 Cl〉 crystals with controlled carrier concentration.__________Translated from Neorganicheskie Materialy, Vol. 41, No. 6, 2005, pp. 656–661.Original Russian Text Copyright © 2005 by Freik, Pysklynets, Mezhylovska.     

砷酸钛氧铷晶体的生长、缺陷和物理性能的研究

采用熔盐法,我们已生长出RbTiOAsO4大单晶。不同取向的晶片经腐蚀后,利用光学显微术,观察了晶体中的生长缺陷。并首次研究了其电光性能和电学性能。结果表明RTA晶体不仅是优良的光学倍频晶体,而且是优良的电光晶体。     

Trapped shallow water waves for continuous bottom topographies

Summary Trapped shallow water waves are studied for gently sloping, continuous bottom topographies. Asymptotic solutions, based on the smallness of the bottom slope are obtained for some two-dimensional and axisymmetric depth functions. Eigenfrequency spectra and corresponding trapped wave patterns are computed.

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Gefangene Seichtwasser-Wellen bei stetigen Bodentopographien

Zusammenfassung Untersucht werden gefangene Seichtwasser-Wellen für sanft geneigte stetige Bodentopographien. Asymptotische Lösungen, basierend auf der Kleinheit der Bodenneigung, werden für einige zweidimensionale und achsensymmetrische Tiefenfunktionen erhalten. Eigenfrequenzspektren und die zugehörigen Wellenbilder werden berechnet.

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With 5 Figures     

Generalized Mean Fields for Trapped Atomic Bose-Einstein Condensates

We describe generalized time-dependent mean-field equations for partially condensed samples of trapped and evaporatively cooled atoms. These equations give a way of investigating the various order parameters that may be present as well as the existence of a mean value of the field due to condensed atoms. Our approach provides us with a closed system of self-consistent equations for the order parameters present. The equations we derive are shown to reduce to other treatments in the literature in various limits. We also show how the equation of motion method allows us to construct a formalism that can handle the evolution of these mean fields due to two-loop kinetics.